1. Field of the Invention
This invention relates generally to metal alloys, and more particularly relates to compositions of certain silver-platinum alloys for use in jewelry and flatware manufacturing.
2. Description of the Related Art
Sterling silver is widely used in the fabrication of jewelry and flatware. It is a metal alloy having a composition typically consisting of at least 92.5% pure silver and about 7.5% copper. Sterling silver is usually provided to jewelry manufacturers in the form of pellet-like shots. The shots can be melted and cast into desired forms using conventional investment casting techniques. Sterling silver is a preferred material for jewelry and flatware largely because silver provides certain desirable properties to the final product, including surface whiteness, malleability, strength, and durability while copper provides other desired properties, such as increased material hardness.
However, one disadvantage associated with sterling silver is that it tends to tarnish easily. It is generally understood that the copper components in the sterling silver alloy tend to react with oxygen to form copper oxide, which typically shows as a darkened area or tarnish in the cast article. Thus, the amount of copper present in the sterling silver alloy can greatly affect the amount of tarnish or blemish appearing on the finished product. In some cases, copper oxide is formed when the sterling silver is still in pellet form, which in turn can cause the tarnish to extend deep into the article during casting and not be easily removed by polishing. In such circumstances, the cast article would have to be scrapped, converted into the elemental metals and then re-alloyed. In view of the foregoing, it will be appreciated that there is a need for an improved silver-based alloy which provides the advantages afforded by sterling silver and yet also has greater tarnish resistance, surface brightness, and increased hardness when compared to sterling silver.